Video Data Analysis
Aim
The aim of this session is to introduce you to the methods of performing quantitative linear kinematic analysis of 2D video data, using the software Quintic Bio mechanics, and Excel.
Objectives
To use Excel to calculate average velocity and acceleration for each shoe condition using the times recorded by the timing lights.
To use 2D video data of participants performing 3 short indoor runs of moderate pace, barefoot and shod, to measure contact and flight time, step length, and cadence, for one full running stride.
Instructions for Analysis
Using Excel:
• Using the Excel spreadsheet (Velocity & Acceleration_Blank.xls), enter the times for one participant’s trials into Table 1 and plot a distance-time graph (Figure 1) for all trials. Draw a smooth curve through the data plots.
• Calculate the average time taken per condition (you will need to enter a formula for this).
• Using the time taken and displacement columns, calculate the average velocity in Table 2 (you will need to enter a formula for this. Remember: Average velocity = displacement / time taken).
• Calculate the average velocity per condition (you will need to enter a formula for this).
• Using the time taken and velocity columns, calculate the change in velocity and the average acceleration in Table 3 (you will need to enter formulas for this. Remember: Average acceleration = change in velocity / change in time).
• Calculate the average acceleration per condition (you will need to enter a formula for this).
Using Quintic:
• Load Quintic Bio mechanics via the Virtual Campus PC, the Start Menu > _Sport Science when on campus, or from the desktop of the computers in the Gallery (Af50) with yellow ‘Quintic PC’ signs on base unit.
• Load the correct calibration object file (see Participant Details spread sheet via link on Blackboard for participants) via the Main tab. Go to the Digitisation tab, and click on Digitisation Menu. Calibrate the video file using the vertical and horizontal scaling objects (1 m rulers) (go to Video File Calibration > Horizontal and Vertical Lines), follow the instructions to draw a horizontal line that matches the length of the metre stick by clicking and holding the left mouse button and releasing at the other end of the metre stick, repeat for the vertical metre stick, and use a recording (sample) rate of 120 Hz when the pop up box asks for the recording rate.
• * Load the video file of your participant’s barefoot middle velocity trial into the software via the Main tab. Go to the Digitisation tab, and click on Digitisation Menu, and select Load external calibration, and load the calibration you have just done (name of calibration object file.hcal or similar).
• Define appropriate markers at key events in the run for one right step in view (you may need to use left step): right foot touchdown (RTD), right foot take-off (RTO), left foot touchdown (LTD). Use the ‘Sprint Phases’ diagrams to help you here.
• Using your event markers RTD and RTO, and the stopwatch tool on the right-hand side of the toolbar, work out the total time the right foot is in contact with the floor and note down in Table 4 as ‘Contact Time’.
• Using your event markers RTO and LTD, and the stopwatch tool on the right-hand side of the toolbar, work out the total time the body is in flight (no foot in contact with the floor) and note down in Table 4 as ‘Flight Time’.
• Using the Shapes tab and vertical line tool, draw a vertical line at the rear of the foot at RTD and LTD events. Use Line Drawing button to draw a line (keeping it horizontal) from the vertical line at RTD to LTD to get right step distance. Note the length (in metres) of the line (look on the bottom right of the screen). Enter into Table 4 as ‘Step Length’.
• Using your event markers RTD and LTD, and the stopwatch tool on the right-hand side of the toolbar, work out the total time taken to perform one step. Divide 60s by this value and note down in Table 4 as ‘Cadence/Step Rate.
• Repeat for the participant’s middle velocity shod trial from *. If you complete this in the IT workshop, repeat for the participant’s other trials. Repeat this for the middle velocity trials for at least 5 participants for your Scientific Communication Poster.
In your write up of this practical as your Scientific Communication assessment your discussion should include the following:
• A discussion of possible experimental difficulties and errors and how you attempted to minimize these;
• An evaluation of how you would use the data you have calculated for providing feedback to your performer for the improvement of their technique / performance.
You need to understand and explain the procedure to calculate displacement, velocity, and acceleration – refer to the lecture notes, formulas in the Excel spreadsheet, and Watkins (2007).
Main Reference
Watkins, J. (2007) An Introduction to Bio mechanics of Sport and Exercise. Chapter 2 – Linear Motion, pp14-23. Philadelphia, PA: Churchill Livingstone Elsevier Ltd.